Data deduplication is a hot topic in storage and saves significant disk space for many environments, with some trade offs. We’ll discuss what deduplication is and where the Open Source solutions are versus commercial offerings. Presentation will lean towards the practical – where attendees can use it in their real world projects (what works, what doesn’t, should you use in production, etcetera).

1. Open Source Data Deduplication
Nick Webb
nickw@redwireservices.com www.redwireservices.com @RedWireServices
(206) 829-8621
Last updated 8/10/2011

2. Introduction
● What is Deduplication? Different kinds?
● Why do you want it?
● How does it work?
● Advantages / Drawbacks
● Commercial Implementations
● Open Source implementations, performance,
reliability, and stability of each

3. What is Data Deduplication
Wikipedia:
. . . data deduplication is a specialized data compression
technique for eliminating coarse-grained redundant data,
typically to improve storage utilization. In the deduplication
process, duplicate data is deleted, leaving only one copy of
the data to be stored, along with references to the unique
copy of data. Deduplication is able to reduce the required
storage capacity since only the unique data is stored.
Depending on the type of deduplication, redundant files may
be reduced, or even portions of files or other data that are
similar can also be removed . . .

4. Why Dedupe?
● Save disk space and money (less disks)
● Less disks = less power, cooling, and space
● Improve write performance (of duplicate data)
● Be efficient – don’t re-copy or store previously
stored data

5. Where does it Work Well?
● Secondary Storage
● Backups/Archives
● Online backups with limited
bandwidth/replication
● Save disk space – additional
full backups take little space
● Virtual Machines (Primary &
Secondary)
● File Shares

6. Not a Fit
● Random data
● Video
● Pictures
● Music
● Encrypted files
– many vendors dedupe, then encrypt

7. Types
● Source / Target
● Global
● Fixed/Sliding Block
● File Based (SIS)

8. Drawbacks
● Slow writes, slower reads
● High CPU/memory utilization (dedicated server
is a must)
● Increases data loss risk / corruption
● Collision risk of 1.3x10^-49% chance per PB
● (256 bit hash & 8KB Blocks)

9. How Does it Work?

10. Without Dedupe

11. With Dedupe

12. Block Reclamation
● In general, blocks are not
removed/freed when a file is
removed
● We must periodically check blocks
for references, a block with no
reference can be deleted, freeing
allocated space
● Process can be expensive,
scheduled during off-peak

13. Commercial Implementations
● Just about every backup vendor
● Symantec, CommVault
● Cloud: Asigra, Baracuda, Dropbox (global), JungleDisk,
Mozy
● NAS/SAN/Backup Targets
● NEC HydraStor
● DataDomain/EMC Avamar
● Quantum
● NetApp

14. Open Source Implementations
● Fuse Based
● Lessfs
● SDFS (OpenDedupe)
● Others
● ZFS
● btrfs (? Off-line only)
● Limited (file based / SIS)
● BackupPC (reliable!)
● Rdiff-backup

15. How Good is it?
● Many see 10-20x deduplicaiton meaning 10-20
times more logical object storage than physical
● Especially true in backup or virtual
environments

16. SDFS / OpenDedupe
www.opendedup.org
● Java 7 Based / platform agnostic
● Uses fuse
● S3 storage support
● Snapshots
● Inline or batch mode deduplication
● Supposedly fast (290MBps+ on great H/W)
● Support for global/clustered dedupe
● Probably most mature OSS Dedupe (IMHO)

17. SDFS

18. SDFS Install & Go
Install Java
# rpm –Uvh SDFS-1.0.7-2.x86_64.rpm
# sudo mkfs.sdfs --volume-name=sdfs_128k
--io-max-file-write-buffers=32
--volume-capacity=550GB
--io-chunk-size=128
--chunk-store-data-location=/mnt/data
# sudo modprobe fuse
# sudo mount.sdfs -v sdfs_128k -m
/mnt/dedupe

19. SDFS
● Pro
● Works when configured properly
● Appears to be multithreaded
● Con
● Slow / resource intensive (CPU/Memory)
● Fragile, easy to mess up options, leading to crashes, little
user feedback
● Standard POSIX utilities do not show accurate data (e.g. df,
must use getfattr -d <mount point>, and calculate bytes →
GB/TB and % free yourself)
● Slow with 4k blocks, recommended for VMs

20. LessFS
www.lessfs.com
● Written in C = Less CPU Overhead
● Have to build yourself (configure && make && make install)
● Has replication, encryption
● Uses fuse

21. LessFS Install
wget http://...lessfs-1.4.2.tar.gz
tar zxvf *.tar.gz
wget http://...db-4.8.30.tar.gz
yum install buildstuff…
. . .
echo never >
/sys/kernel/mm/redhat_transparent_hugepage/defrag
echo no >
/sys/kernel/mm/redhat_transparent_hugepage/khugep
aged/defrag

22. LessFS Go
sudo vi /etc/lessfs.cfg
BLOCKDATA_PATH=/mnt/data/dta/blockdata.dta
META_PATH=/mnt/meta/mta
BLKSIZE=4096 # only 4k supported on centos 5
ENCRYPT_DATA=on
ENCRYPT_META=off
mklessfs -c /etc/lessfs.cfg
lessfs /etc/lessfs.cfg /mnt/dedupe

23. LessFS
● Pro
● Does inline compression by default as well
● Reasonable VM compression with 128k blocks
● Con
● Fragile
● Stats/FS info hard to see (per file accounting, no totals)
● Kernel >= 2.6.26 required for blocks > 4k (RHEL6 only)
● Running with 4k blocks is not really feasible

24. LessFS

25. Other OSS
● ZFS?
● Tried it, and empirically it was a drag, but I have no
hard data (got like 3x dedupe with identical full
backups of VMs)
● At least it’s stable…

26. Kick the Tires
● Test data set; ~330GB of data
● 22GB of documents, pictures, music
● Virtual Machines
– 220GB Windows 2003 Server with SQL Data
– 2003 AD DC ~60GB
– 2003 Server ~8GB
– Two OpenSolaris VMs, 1.5 & 2.7GB
– 3GB Windows 2000 VM
– 15GB XP Pro VM

27. Kick the Tires
● Test Environment
● AWS High CPU Extra Large Instance
● ~7GB of RAM
● ~Eight Cores ~2.5GHz each
● ext4

28. Compression Performance
● First round (all “unique” data)
● If another copy was put in (like another full), we should expect
100% reduction for that non-unique data (1x dedupe per run)
FS Home % Home VM % VM Combined % Total MBps
Data Reduction Data Reduction Reduction
SDFS 4k 21GB 4.50% 109 64% 128GB 61% 16
GB
lessfs 4k 24GB -9% N/A 51% N/A 50% 4
(est.)
SDFS 128k 21GB 4.50% 255 16% 276GB 15% 40
GB
lessfs 128k 21GB 4.50% 130 57% 183GB 44% 24
GB
tar/gz --fast 21GB 4.50% 178 41% 199GB 39% 35
GB

30. Write Performance
(don't trust this)
MBps
40
35
30
25
20 MBps
15
10
5
0
raw SDFS 4k lessfs 4k SDFS 128k lessfs 128k tar/gz --fast

31. Kick the Tires: Part 2
● Test data set – two ~204GB full backup
archives from a popular commercial vendor
● Test Environment
● VirtualBox VM, 2GB RAM, 2 Cores, 2x7200RPM
SATA drives (meta & data separated for LessFS)
● Physical CPU: Quad Core Xeon

32. Write Performance
MBps
40
35
30
25
20 MBps
15
10
5
0
raw SDFS 128k W SDFS 128k Re-W LessFS 128k W LessFS 128k Re-W

34. Load
(SDFS 128k)

35. Open Source Dedupe
● Pro
● Free
● Can be stable, if well managed
● Con
● Not in repos yet
● Efforts behind them seem very limited, 1 dev each
● No/Poor documentation

36. The Future
● Eventual Commodity?
● brtfs
● Dedupe planned (off-line only)

37. Conclusion/Recommendations
● Dedupe is great, if it works and it meets your
performance and storage requirements
● OSS Dedupe has a way to go
● SDFS/OpenDedupe is best OSS option right
now
● JungleDisk is good and cheap, but not OSS

38. About Red Wire Services
If you found this presentation helpful, consider
Red Wire Services for your next
Backup, Archive, or IT Disaster Recovery
Planning project.
Learn more at www.RedWireServices.com

39. About Nick Webb
Nick Webb is the founder of Red Wire Services, in
Seattle, WA. Nick is available to speak on a variety of IT
Disaster Recovery related topics, including:
● Preserving Your Digital Legacy
● Getting Started with your Small Business Disaster
Recovery Plan
● Archive Storage for SMBs
If interested in having Nick speak to your group, please
call (206) 829-8621 or email info@redwireservices.com